Nope, if it only happened once a long time ago, I can understand how they would feel bad that they're still being blamed for it. But, they also need to understand that I would never date anyone with a cheating history regardless of how long ago it was.
Nope. Not a chance in hell. Cheating is rarely pre-meditated, it's usually a moment of weakness that results in cheating but regardless of their attempted justification, I wouldn't be able to be with someone who would always leave me with a bit of doubt in the back of my mind.
Chances are I won't know about it, and why would I? It doesn't concern me. Whether or not she's changed will be apparent after a while of seeing her. She deserves to start on a clean slate, question is, how clean can she keep it.
It really depends, I would ask at what age did you cheated, why did you cheated, and what kind of person is this girl and her past boyfriend is. I would like to know the full story and maybe I would date her with a cheating history.